Microphone



w. R. LANE MICROPHONE April 19', 1932.

Filed May 51, 1930 INVENTOR ATTORNEY Patented Apr. 19, 1932 wILLI-n vrnon IJAnE, or NIAG This invention relates to microphones an class which are emp mitters although the inven means restricted t primary objects of the pre to provide gree of st so that the in same degree of elficiency and in all posi Another obj ec vide a mic sensitivity suitable adjustment to a ciency wlth a re tion.

Another object o vide a microphone ple in its construct crophone of high manufactured ent parts readily assemble Generally speaking,-

in an improvemen electrodes ployment o tween the sessing none of thedisa 2"; i granul t1on an d which, as is well Application filed m 31,

loyed a 0 this use,

ami ability an strument W1 d freedom tions.

rophon quality at a low co t in the constr of a microphone f a novel mate rdinarily empl ency to pack.

In developing into consideration I 7 between contact poin their elasticity, then such a panied by the partic imposed. In sectional di-mens ies, under that if or c ction w some shortening les along the a mechanical pressure,

at the same time, along the axis 0 d also be decreas cal resistance. n mech terial, would pr other words, the norm improvements in d more particularly to that s telephonic transtion is not by any and one of the sent invention is crophone possessing a high defrom caking ll operate with the dependability t of the invention is to proe which may possess a high and which may be controlled by high degree of ellilatively low current consumpf the invention is to prowhich will be more simion'than the ordinary miand which maybe st and its compond and adjusted.

the invention resides uctio and in the emrial ormedium beand movable electrodes posdvantages o oyed in this connecknown have a tendmy invention I have taken microphonic action ts or surfaces is dueto hange in contact area, ould necessarily be accomor contraction of Xis of the stress al cross ionof two contractin would the dimension f the applied ed, and both ditions would result in a de- It is anical pressure ap oduce a given d thereforelf.

f carbon ns PATENT, rice A A ALLS W YORK: nrcnornonn 1930. Serial No. 458,147.

its dimension in the line of pressure were very small, then the decrement percentage-ofthis dimension under given mechanical pres sure, would be proportionately great. 7

I have discovered that if two; iron balls 58' were provided with an externally thin coatmg film of carbon and were brought into contact, that their microphonic response to mechanical pressure would he unusually-pro- I nounced. The iron core of eachball having 60- a resistance wholly negligible in comparison to the carbon coating, would serve merely as a low resistance conductor. Inot'her-words, virtually the entire resistance of such anar rangement would reside in the pointsofcontact at all times, a desideratum in the design of-an ideal microphone. However, in order that such a medium might be employed in accordance with the purpose of the present invention, 1' have found that a more desira- 7o ble resistance would be obtained by the use, as such a medium, of small magnetic pan ticles, suitably graded, which particles are coated with carbon by sifting them through the hot flame of a gasoline blow-furnace, 76 thereby heating them to incandescence and automatically quenching them as they fall into the hydro carbon liquid in the priming cup below the blow flame. But first, and after extended experiment, it was found necessary to electro-plate the small magnetic particles with silver as a sort ofpr-im-ing coat, for it was discovered that in noother way, apparently, was it possible to avoid the formation of anoxide coating or fi'lm 85 underneath the carbon coating, and'this in turn interposedsuch as inordinately high electrical resistance as to defeat the purpose: of the schem The reason for resorting to. silver as a plating medium was due to the 9 fact that silver oxide, if'formed, has substan tially the same conductivity :as the base. silver, which is of notably low. resistance. While this coatingv wassuccessfully accom: plished by me, it isconceivable thatitmight 95 be obtainable by other methods.

I further found that; if suchv silver and; carbon :coated magnetic particles weresubstituted for the said earbomg-ranules originally; employedin the common typeof microphone 9 n of the g, bodbe inbelived plied and that if a rear or stationary electrode could be mounted on one pole of a magnet, I could obtain a microphonic increase by the present invention.

This invention also consists in certain other features of construction and in the combination and arrangement of the several parts, to be hereinafter fully described, illustrated in the accompanying drawings and specifically pointed out in the appended claims, it being understood of course that minor changes may be made so long as they fall within the scope of the claims.

In describing my invention in detail, reference will be had to the accompanying drawings, wherein like characters denote like or corresponding parts throughout the several views, and in which Figure 1 is a vertical front to rear sectional view through a telephonic microphone embodying the invention.

Figure 2 is a vertical transverse sectional view taken substantially on the line 22 of Figure 1, looking in the direction indicated by the arrows.

Figure 3 is a detail view on an enlarged scale, illustrating schematically the character of the carbon coated electro-magnetic particles as they will be assembled between the fixed and movable electrodes of the microphone.

Figure 4 is a sectional view on an enlarged scale illustrating one of the carbon coated electro-magnetic particles prepared by a process somewhat different from that by which the particles shown in Figure 3 are formed.

In the drawings the numeral 1 indicates in general the ordinary hard rubber mouth piece of a telephone transmitter embodying the invention and the numeral 2 indicates the front of the shell of the microphone casing, the rear part of the shell or the body thereof being indicated by the numeral 3. The numeral 4 indicates a lock ring for clamping in place the diaphragm of the microphone which is indicated by the numera-l 5, and which may be'the ordinary type of diaphragm.

A soft rubber band 6 is disposed to embrace the periphery of the diaphragm 5 and is confined between the front piece 2 of the shell and the locking ring 4, and serves effectively to insulate and at the same time cushion the iaphragm 5. The body 3 of the shell is formed in its inner side at its rear with a threaded socket 7, and the threaded end 8 of a permanent magnet 9 is fitted into the socket and held against rotative displacement by a set screw 10. The numeral 11 indicates an insulating sleeve of bakelite, which is interiorly threaded at its rear end and fitted onto the forward end of the permanent magnet 9. This permanent magnet constitutes the fixed electrode of the microphone and the movable electrode is indicated by the numeral 12 and comprises a circular body portion 13 having an outstanding circumscribing flange 14 at its forward end. The body 13 of the movable electrode is of a movable diameter to fit within the forward end of the bore of the sleeve 11. The numeral 15 indicates carbon disks, one of which is in engage-- ment with the forward end of the magnet 9 and the other in engagement with the inner end of the body 13 of the movable electrode, and the filling 16, of metallic magnetic particles coated with carbon is arranged between the disks 15.

A ball 17 of magnetic material is seated in a socket formed centrally in the outer end of the movable electrode 12 and presses against the diaphragm 5 at the center thereof. A helical spring 18 which may consist of a few turns of small wire, of suitable material and dimensions, is preferably arranged between the inner side of the flange 14 of the movable electrode within the recess 19, thusproviding a resilient spacing means between the movable electrode and the fixed electrode, and also functioning as a centering and aligning device for the body 13 of the movable electrode 12.

As stated, Figure 3 of the drawings illustrates, on a much enlarged scale and schematically, the magnetic metal particles which are coat-ed with carbon, and in this figure the numeral 20 indicates the individual particles, of magnetic metal and the numeral 21, thecoating of carbon which is formed thereon by the method above described or any other practical method.

In the embodiment of the invention shown in Figure 4 of the drawings, the medium between the electrodes of the microphone differ somewhat from the material previously described and shown in Figure 3 in that, in addition to selecting suitably graded particles of magnetic material and shifting them through the hot flame of a gasoline blowfurnace, thereby heating them to incandescence and automatically quenching them as they fall into the hydro-carbon liquid in the priming cup below the blow-flame, I have found that if silver and carbon coated mag netic particles are substituted for the carbon granules ordinarily employed, and if the rear or stationary electrode could be mounted upon one pole of a magnet I could obtain a microphonic increase more effectually than by the mere carbon coating of the particles and, as shown in Figure 4, one of the individual particles is indicated by the numeral 22. and the deposit of silver, which deposit is indicated by the numeral 23 is effected by electro-plating the small magneticv particles with silver. The carbon coating is indicated by the numeral 2 and it will be understood that the silver coating 23 constitutes in effect a priming coating which avoids the formation of an oxide coating or film beneath the carbon coating 24, and I have found it desirable to employ silver as a plating medium in view of the fact that if oxide of silver is formed it has substantially the same conductivity as the silver itself, the silver having a notably low resistance.

While all of the metal parts in the embodiment of the invention, except, possibly, the

resilient spacer 18, shown in the present drawings are of magnetic material, this is true for the reason that I thought it desirable to provide a substantially closed magnetic circuit. It is conceivable, however, that an open magnetic circuit might be employed, in which case, an aluminum diaphragm and other parts might be substituted for the other parts, which are of another metal, in the illustrated embodiment of the invention, with the exception of the magnet. The aluminum diaphragm may be employed in any event if it were deemed of importance to do so without introducing a very large air gap into the magnetic circuit. Also the magnet might be an electro-magnet instead of a permanent magnet, if this construction would be considered advantageous, and in this case, the magnet would be energized by the line circuit as are the so-called D. G. telephone receivers used in a common battery system.

A conductor wire 25 from a source of current is led through a sleeve 26 mounted in the wall of the body 3 and connected to the movable electrode 12.

What I claim is 1. In a microphone, a magnet constituting the fixed electrode, and an armature constituting the movable electrode, a diaphragm, a magnetic element upon the movable electrode contacting the diaphragm, carbon disks disposed against the end of the magnetand against the opposing face of the movable electrode, the said mass of carbon coated magnetic particles filling the space between the said disks, a helical spring interposed between a flange upon the movable electrode and the adjacent end of said sleeve and constituting a resilient means for yieldably holding the said element upon the movable electrode in contact with the diaphragm.

2. In a microphone, a magnet constituting the fixed electrode, and an armature constituting the movable electrode, a diaphragm, a magnetic element upon the movable electrode contacting the diaphragm, and a mass of carbon and silver coated magnetic particles interposed between the fixed and movable electrodes.

In testimony whereof I affix my signature.

WILLIAM ROE LANE. 

